Rotary compressors have been widely used for compressing refrigerant in refrigeration systems such as refrigerators, freezers, air conditioners, and the like. A typical rotary compressor comprises a housing in which a motor and a compressor cylinder block are disposed. The motor drives a crankshaft for revolving an orbiting piston ("roller") inside a bore of the cylinder. One or more vanes are slidably received in corresponding slots located through the cylinder walls. The vanes separate areas of suction pressure from areas of discharge pressure and, thus, cooperate with the rotor and cylinder wall to provide the structure for compressing refrigerant within the cylinder bore. A representative rotary compressor is described in U.S. Pat. No. 5,374,171, which is incorporated by reference.
One problem encountered with rotary compressors has been the high frictional loading between the vane tip and the roller. To maintain compressor efficiency, the vane has to be highly loaded against the roller in order to prevent refrigerant leakage from high pressure areas to low pressure areas. As a result, the interface between the vane tip and the roller tends to be subject to a substantial amount of friction. If this friction is not minimized, the roller and/or the inner tip may tend to wear out too quickly. This is undesirable, because a compressor having a worn roller or a vane with a worn inner tip may perform poorly. In some instances, if the wear is severe enough, the compressor may not even be operational.
Most commonly, this friction has been controlled by lubricating the interface between the vane tip and the roller with oil. In order for the oil to be distributed to this interface, as well as to other points of the compressor which require lubrication, the oil must have substantial solubility and miscibility with the refrigerant. In this way, as the refrigerant moves through the compressor, the refrigerant carries the oil with it.
Previously, chlorine containing refrigerants and oils compatible with such refrigerants were widely used in rotary compressors. Due to environmental concerns, however, the use of such chorine containing refrigerants will soon be prohibited. As a result, these refrigerants have been replaced by newer, non-chlorine containing refrigerants. Unfortunately, the oils that were used in combination with the chlorinated refrigerants do not have adequate solubility/miscibility with the non-chlorinated refrigerants. This deficiency means that the oil is not carried through the system by the refrigerant, which hinders oil return from the system to the compressor. Effective lubrication cannot be achieved. In order to provide effective lubrication, polyolester oils, which have adequate solubility and miscibility with the newer refrigerants, have been developed and are now currently used in combination with non-chlorinated refrigerants.
The use of the polyolester oils in rotary compressors, however, has been problematic. As one problem, the polyolester oils are not as lubricious as the oils that had been used with the chlorinated refrigerants. Due to such reduced lubricity, the vanes and roller of some rotary compressors may tend to wear at a faster rate when the new refrigerants/polyolester oil combinations are used. Accordingly, it would be desirable to improve the lubrication of such compressors so that the roller and/or vanes show better wear characteristics.
As another drawback, under conditions of excess wear, the refrigerant passages of some rotary compressors may have a tendency to plug up when polyolester oils are used for lubrication. A rotary compressor with plugged up passages not only performs poorly, but also, in many instances, the plugged up passages can damage, or ruin the compressor, requiring costly repair or replacement. Accordingly, it would be desirable to develop an approach that alleviates this problem.